The present invention relates to a controllable vibration damper.
Vibration dampers having adjustable characteristics are known. The mechanism for adjustment of the damping force changes the flow openings for the directions of compressive and trajectory motion. It is conventional practice in the prior art to have a predefined set of diaphragms or throttles for this purpose, which will be chosen and activated singularly or in combination as required. Various designs have been used in this respect.
One system is based on a perforated disc which is twisted electromotively, such that flow passage openings of differing flow resistance are chosen. The number of different openings corresponds directly to the number of different discreet damping stages.
Another system is based on non-adjustable, permanently effective flow passage openings connected in parallel with further flow passage resistances for the purpose of adjusting the damping force. The respective totals flow resistance resulting will then determine the damping effect. The number of possible combinations of total resistances dictates the number of possible damping stages.
The adjustment speeds between the individual stages are different, depending on the principle of adjustment. Valve reaction times in the range of 10 millisecs are referred to as `quick`, in the context of the above statements, in contrast to other adjustment mechanisms with a reaction time in the range of 50 millisecs up to several seconds which are rated as `slow`.
There are system embodiments which permit selection by switches of different stages of comfort (e.g., `sportive-hard sprung`, `normal`, `softly sprung`, etc.). Other system embodiments are existing in which this change-over of ranges is performed automatically according to predefined speed and acceleration thresholds. The latter are referred to as `controlled dampers`. For reaction to speed limits, slow actuators are sufficient. For reaction to impacts, short-term high accelerations, fast actuators are required. The only advantage of speed-responsive slow control actions is increased driving comfort. The advantage of quick controlled dampers lies in the possibility of augmenting the driving comfort to a maximum and changing over for a short time to maximize driving safety in the instance this is needed.
Due to the coarse adjustment stage, all previous technical solutions presently permit merely actuating working points on a limited number of predetermined characteristic curves within the plane of the possible range of use. That means, none of the present technical solutions complies with the necessity of being able to react correspondingly finely to an acceleration signal having a sufficient sensor resolution. Yet, a high resolution would be advisable from a technical point of view in order to be able to sensitively react to the demand for damping with a view to ensuring driving safety. If the interests of comfort play the predominant role, practice has proven that the untrained user is not in a position to make a distinction between more than three stages of hard suspension. In the majority of cases, the untrained user only feels the difference in comfort between `extremely hard sprung` and `extremely softly sprung`. Moreover, tests with quick controlled dampers have proven that the damping system remains automatically in the `comfort stage` for approximately 90% of the driving time and changes over to `safety stage` for roughly 10% of the driving time. It is remarkable in this regard that the medium stages are required only for a short time, as transition stages so-to-speak. (Of course, this applies only for ranges of normal speed; at high speeds, `hard sprung` damping is formed for reasons of safety!).